In all fairness, many Swedish homes were poorly insulated at least up until the 60's. My grandparents house still had single glass windows, heating only on the lower floor and no bathroom when they sold it a few years ago.
The Swedish economy boomed after WWII and many homes were built in the decades that followed. These are typically very well insulated and heated. A lot of work was also put into improving insulation and adding heating to existing homes. In fact, a recent study suggested that there had been no further improvement since 1980.
The latest homes have no heating, only very thick walls. Surprisingly it seems to work.